In wireless communication networks, UEs (User Equipments), communicate data via radio base stations.
In this description, the term “User Equipment” will be used to denote any suitable communication terminal adapted to communicate with a radio base station. A UE may be implemented as a mobile phone, a PDA (Personal Digital Assistant), a handheld computer, a laptop computer, etc. A “radio base station” may be implanted as a NodeB, an eNodeB, a repeater, etc.
In “heterodyne” receiver structures, an incoming RF-signal is fed into a first input of a mixer where it is mixed with a local oscillator (LO) frequency which is fed into a second input of the mixer. The mixer output is a down-converted version of the RF-signal of an intermediate frequency, where the LO frequency is removed from the incoming RF-signal, i.e. the RF-signal spectrum is transferred into an IF (Intermediate Frequency) spectrum.
In double conversion systems, which are common today, a received RF-signal spectrum is frequency converted in two steps before the signal is fed into a receiver arrangement. First the received RF-signal is frequency converted from a RF frequency range into a lower first IF frequency range, and then the first IF frequency range is frequency converted into a second IF frequency range, before being A/D (Analogue-to-Digital) converted and fed into the receiver arrangement.
With reference to FIG. 1, which is a schematic overview, a situation where UEs are arranged to communicate data in a wireless communication network according to the prior art will now be described.
A first UE 104 is present in a first cell 102 of a wireless communication network. The first UE 104 communicates data with a first radio base station 100 which serves the cell 102. A second UE 114 is present in a second cell 112 of the wireless communication network. Correspondingly, the second UE 114 communicates data with a second radio base station 110 which serves the second cell 112.
In general, in cellular communication networks the cells overlap each other, especially at the cell borders. There are situations where UEs are located closer to other radio base stations than the UEs which these other radio base stations are communicating data with. The radiation emitted from such a UE may reach a “wrong” radio base station, to which this emitted radiation is an interfering disturbance.
In the situation described above with reference to FIG. 1, the UE 114 is communicating data with the radio base station 110. However, since the UE 114 is located closer to the radio base station 100 then the UE 104 which communicates with the radio base station 100, the emitted signal from the UE 114 that reaches the radio base station 100 could be stronger than the emitted signal from the UE 104. This is especially the situation when the UEs are located near the cell borders, and the power level of the emitted radiation of the UE 114 is high. The emitted radiation from the UE 114 which reaches the radio base station 100 is perceived as interference noise by the first base station 100, and because the UE 114 is located much closer to the radio base station 100 than the UE 104 the interference signal may be much stronger then the data signal of the UE 104.
In heterodyne receiver arrangements of wireless communication networks, received RF-signals are commonly frequency converted in two steps before being A/D-converted (Analogue to Digital) into a base band, so called double conversion. The received RF-signals are then mixed with an output signal of an RF LO into an Intermediate Frequency (IF) signal in a first step. Then, in a second step, the IF-signal is mixed with an output signal of an IF LO into a second IF-signal.
With reference to FIG. 2, which is a schematic graph, some definitions of bandwidths will now be described in accordance with the prior art.
When communicating data in uplink UL (uplink) operating bands are reserved, e.g. the frequency range 1850-1910 MHz is reserved by the 3GPP (Third generation partnership project) for UL transmission. However, all base stations and UEs are not capable to make use of the full UL operating band when communicating. In general, a maximum RF (Radio Frequency) bandwidth which is able to apply for a BS when communicating with a UE is narrower or equal with the UL operating bandwidth. The maximum RF bandwidth is also referred to as IBW (Instantaneous Bandwidth) within literature. For a receiver, the width of IF filter passband are normally same as IBW to provide good rejection to interference. In multi carrier base stations and UEs, a number of carriers are contained within the maximum RF bandwidth. For instance, as illustrated in FIG. 2, a maximum RF bandwidth of 60 MHz, may contain 2 carriers of 20 MHz each. In this case, the RF bandwidth, which is from lower edge of carrier 1 to higher edge of carrier 2, is narrower than IBW.
There is a problem that base stations are affected by interfering RF-signals from other radio base stations or UEs, and there is a need for more robust receiver arrangements.